Electric meter.



' No. 856,412. PATENTED JUNE 11, 1907.

.A. J.'MARTIN.

ELECTRIC METER. APPLIOATIGN rum) ROV.2, 1906.

WIT NE 555' 5' I 1N YEN TUE ATTY.

UNITED; sTATns PATENT OFFICE.

ARTHUR J. MARTIN, OF. RUGBY, ENGLAND, ASSIGNOR To GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC METER.

- Specification of Letters Yatent.

Patented June 1 1, .1907.

Application and November 2,1906. $erial No. 841,777.

. pressed a voltageproportional to ;the loadthe loadcurrent.

its range this proportionality is maintained,

current. The accuracy of registration of a meter of this ty e depends upon the counterelectromotive Earce of the armature, and consequently the speed, remaining exactly proportional to the Impressed voltage and to Over the. greater, part of so that on full'load the registration of the meter is accurate, but on light loads, owing to greater proportional effect of friction and t e I o%her losses the speed'of the meter falls below roper value. he object of my invention is to im rove the accuracy of such meters on light oads, and broadly consists in providing means for producing a weakening of the field-strength on light loads. This weakening of fieldstrength decreases the counter-electroinotive force per revolution, and consequently increases the speed of the meter.

More specifically stated, my invention consists in providing'an auxiliary yoke for the its fi el d magne with a magnetizing winding supplied wit current proportional to the load-current. This yoke is arranged to be saturated at a fraction of full load, and the magnetizing coil is so connected. that the magnetism of the auxiliary yoke assists the magnetism of the main yoke. Since over the greater part of the range of the meter the auxiliary yoke is saturated, the field strength of the meter remains ractically constant, just as though the aux" iary oke were not present; but when the load fa ls below a certain limit, the magnetism of the auxiliary yoke falls below the point of saturation and a decrease of load below this point results in a weakening of the field-strength of the meter. The speed of the meter is consequently in creased, and its accuracy on light loads improved.

My invention will best'be understood by reference to the accompanying drawing, inwhich Figure 1 shows an elevation of a meter arranged in accordance with my invention;

, and Fig. 2 shows a plan view of the same.

magnet of the meter, which comprises a pair of fieldoles and a yoke of constant magnetic strengtli This yoke may be either a permanent' magnet or may be magnetized from an% suitable constant-current source.

and which drives the registering train indicated by the gear 0..

D represents an auxiliary yoke, which is the main yoke, and which carries a magnetiz with the meter armature.

The terminals of the armature circuit are laced in series with the conductors G formmg the circuit which is to be metered.

' The operation of the meter is as follows: Since the armature is connected in shunt to the resistance F, it 'has impressed on its terminals a voltage proportional to the ohmic dro in the resistance, and. conse uently to thelbad-current in the circuit G. herefore, with a constantfield-strength, the armature will tend-to rotate at aspeed proportional to the load-current, in order to produce a counter-electromotive force a proximately equal to the voltage impresse on the armature. Over the greater part of its range the proportionality of armature speed to load-current remains practically cbhstant with a uniform field-strength, but on light loads, if the fieldstrength were maintained constant, the armature-s eed would fall below its proportional va ue. I

The magnetizing winding E which carries a current proportional to the load-current, acts to weaken the field winding on light loads in the following Way? The core D is arranged to be saturated ata fraction of full load, so that over the greater part of the range of the meter the coil E does not effect theconstanc of magnetization of the fieldmagnet. Y en the load falls below a .ccr tain point, the magnetization of the auxiliary yoke D; falls below the saturation point, and since the coil E is arranged to assist the mag- In the drawings, A represents the fieldconnected to the field-poles in parallel with represents the meterarmature, which is rotatably mounted between the field-poles ing coil E which may be connected in parallel connected across a resistance F, which 18 netization or the main yoke", a further de crease of the load-currentresults in weakening the eflective field-strength oi the meter. The speed of the meter on light loads is consequently increased and the accuracy of the meter improved.

I do. not desire to limit myself to the particular construction and arrangement of parts here shown, but aim invthe appended claims to cover all modifications which are Within the scope of my invention. 7

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. An electric meter comprising a field ofsubstantially constant strength on full load, a rotatable armature, connections for supplyingto said armature a voitage. proportional to the load-current, a registering train driven by said armature, and means for producing a decrease in the strength of said field on light load.

2. An electric meter comprising fieldpoles, a main yoke of constant magnetization joining said poles, an armature rotatably mounted between said poles, connections for I supplying to said armature a voltage proportional to the load-current, a registering train driven by said armature, an auxiliary yoke joining said field-poles, and means for apply ing to said auxiliary yoke a magneto-motive proportional to the load-current, said force yoke 7 fraction of full load.

3. An electric meter comprising field-poles, a main yoke of constant magnetization oining said poles, an armature rotatably mounted between said poles, a registering train driven by said armature, an auxiliary yoke joining said field-poles, a magnetizing Winding for said auxiliary yoke, and connections 7 for supplying both to the armature and to said magnetizing Winding voltage proportional to eingarranged to be saturated atathe load-current, saidyoke being arranged to be saturated at a fraction of full load.

4. In combination with an electric circuit and a resistance in series therewith, a meter for said circuit comprising a field ma net of substantially constant strength on fa? 1 load,

a rotatable armature connected in shunt to said resistance, a registering train driven by said armature, and means for roducinga decrease in strength of saidfielcf magnet on light load. I

5. In combination with an electric circuit and a resistance in series therewith, a meter for said circuit comprising field-poles, a main yoke of constant magnetization joining said poles, an-armature rotatably mounted between said poles and connected in shunt to w i said resistance, a registering train drivemby said armature an auxiliary yoke joining said field-poles, and a magnetizing winding for said auxiliary yoke connected in circuit with I the armature,- said auxiliary yoke beingar- AQJ. MARTIN.

Witnesses:

CHARLES W. FULLER, J W. FOSTER.

rotatable armature, connections for supplymy hand this fifteenth day of October, i). 

